GB1576524A

GB1576524A - Process and kit for the determination of transcobalamins

Info

Publication number: GB1576524A
Application number: GB22317/77A
Authority: GB
Original assignee: Yissum Research Development Co of Hebrew University of Jerusalem
Current assignee: Yissum Research Development Co of Hebrew University of Jerusalem
Priority date: 1976-05-26
Filing date: 1977-05-26
Publication date: 1980-10-08
Also published as: IL49662A0; DE2723644A1; FR2353061A1; JPS52154698A; IL49662A

Description

(54) PROCESS AND KIT FOR THE DETERMINATION OF TRANSCOBALAMINS (71) We, YISSUM RESEARCH DEVELOPMENT COMPANY, an Israeli body corporate, of The Hebrew University of Jerusalem, Israel, do hereby declare the invention for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: Human serum contains at least three known binders of Vitamin B-12, namely the three transcobalamins designated as TC-I, TC- II, and TC-III. TC-I and TC-III are derived from granulocytes and both are alpha-globulins with a similar molecular weight, of about 120,000.

They have a different electrical charge and hence differ in their electrophoretic mobility.

TC-II is a beta-globulin of molecular weight of about 38,000 and it is derived mainly from the liver. The physiological functions of the three transcobalamins are not fully understood, but it is known that endogenous Vitamin B-12 is bound mainly to TC-I (about 85it), and TC-II binds about 15 % of endogenous B-12 while TC-III seems to bind Vitamin B-12 only in vitro.

Since TC-II binds small quantities of endogenous B-12 while it takes up the main part of Vitamin B-12 added to the serum in vitro, most of the unsaturated B-12 binding sites are located on TC-II (unsaturated B-12 binding capacity, UBBC). Vitamin B-12 is bound in the serum to the transcobalamins in a 1:1 molar ratio.

It is well known that certain pathological conditions are associated with significant specific changes in the level of the three transcobalamins in serum and that the determination of the Vitamin B-12 binding capacity of each of the three transcobalamins is an important tool in medical diagnosis. Amongst others, the quantitative determination of the B-12 binding capacity of the three transcobalamins is of value in the effective screening of certain malignant diseases and also in the monitoring of the treatment of these diseases. Amongst others, the determination of three transcobalamins is of value in: A. Diagnosis, evaluation of treatment and monitoring of the course of myeloproliferative diseases [CML (chronic myelocytic leukemia), APL (acute promyeolocytic leukemia), polycythemia vera.] B.Differentiation of leukemoid reactions and conditions manifested by non-leukemic leukocytosis.

C. Recognition of rapid malignant cell proliferation in lymphoma, sarcoma, Hodgkins Disease, acute leukemia, etc.

D. Evaluation of therapy and monitoring the course of malignant diseases (remission and relapse) such as sarcomas, acute leukemias, Hodgkins Disease, lymphomas etc.

E. Diagnosis and recognition of hepato-cellular damage.

The quantitative determination of B- 12 binding capacity of the three transcobalamins may also be of value in the recognition, differentiation and monitoring of various other disorders.

The three transcobalamins present in human serum are difficult to separate and their quantitative determination is both complicated and time-consuming. The main problem is the similarity of electrophoretic properties of TC-II and TC-III and their similar behaviour on DEAE-cellulose separation.

The known determinations require at least two steps, namely: a. DEAE-cellulose chromatography to separate TC-I from TC-II and TC-III and a "Sephadex" (REGISTERED Trade Mark) G-200 column to further separate TC-II from TC-III; b. Adsorption of TC-II on charcoal and subsequent separation of TC-I and TC-III by a DEAE-cellulose chromatography; c. Selective removal of TC-II from serum by Quso G-32 (a microfine precipitated silica) and subsequent separation of TC-I from TC-III on DEAE-cellulose; d. Separation of TC-II on a G-200 column and subsequent separation of TC-I from TC-III by a DEAE-cellulose column.

e. Selective removal of TC-II by precipitation with ammonium sulfate and further separa tion of TC-I and TC-III from each other by DEAE-cellulose chromatography.

The above mentioned two-step procedures are rather laborious and require from two to three days to complete. Thus these are actually tools of a research laboratory and indeed the known procedures have not gained widespread acceptance as routine laboratory method in clinical laboratories.

The present invention provides a simple and rapid process for the fractionation of the three transcobalamins in serum from each other and for their quantitative determination. It further plovides a kit for carrying out this fractionation and determination.

The process of the present invention for the quantitative determination of each of the three transcobalamins TC-I, TC-II, and TC-III in serum comprises incubating a predetermined quantity of serum with a solution of 57Co Vitamin B-12, passing the resulting solution at a pH of about 8.5 through adsorption means adapted to selectively adsorb TC-II in the form of a filter of cellulose carrying highly polar substituents or of a small adsorption column; adsorbing the TC-I and TC-III constituents of the resulting solution on a filter or small column of DEAE-cellulose (i.e. diethylaminoethyl-cellulose); selectively desorbing the TC-III using a monopotassium phosphate solution of about 0.05 M and a pH of about 4.6, and determining the radio-activity of each of the three transcobalamin fractions thus obtained, indicating the individual and total unsaturated B-12 binding capacity (UBBC) of the three transcobala mins. The adsorption means adapted to selectively adsorb TC-II is preferably a filter of cellulose nitrate but filters of other cellulose derivatives carrying highly polar substituents can be used and such filters can be replaced by small adsorption columns (hereinafter referred to as mini-columns) fulfilling the same function. Similarly the TC-I and TC-III are preferably adsorbed on a filter of DEAE-cellulose but a mini-column fulfilling the same function can be used.The entire procedure whether using filters or mini-columns is carried out in a rapid and continuous sequence of steps which can be completed within about one hour and a plurality of samples can be tested simultaneously.

Before passing the reaction mixture through the filters or min-columns, the reaction mixture is incubated with an excess of 57Co Vitamin B-12 of high specific activity at a pH of about 8.5 and preferably in a sodium borate buffer of about 0.1 M having a pH of about 8.5.

The radioactivity of the individual three transcobalamin fractions is determined and this gives a quantitative measure of the Vitamin B-12 binding capacity of each of the three trans cobalamins. The adsorptions and desorptions are both specific and quantitative and thus provide a test of high accuracy and entirely adequate for clinical purposes.

The invention is described in the following Example only in an illustrative manner, and it is clear that various modifications and changes can be resorted to in the details of the means used for the separation procedure.

I. MATERIALS 1. Cellulose nitrate filter discs, 25 mm in diameter (Schleicher and Schull, Dassel, Ger many).

2. DEAE-Cellulose (DE-81) filter discs, 25 mm in diameter (The Whatman Biochemicals Ltd., Maidstone, Kent, England).

3. 'Millipore' (Registered Trade Mark) type filter holder apparatus for 25 mm discs (The Tamar Co., Jerusalem, Israel).

4. 57Co B-12, high specific activity (135-200 uCi/ug, the Radiochemical Centre, Amer sham, Bucks, England). Batches of 10 uCi were diluted with water to a final concentra tion of 10,000 pH B-12/ml and stored in the refrigerator until ready for use.

5. Borate buffer, 0.1 M Sodium Borate adjusted to pH.8.5 with 10M NaOH, prepared in glass distilled water and filtered through cellulose-nitrate filter to remove particles that may interfere with the assay.

6. Phosphate solution, 0.05 M monopotassium phosphate (pH 4.6) prepared in glass distilled water, and filtered through cellulose-nitrate filter as described above. The concentration of the phosphate is quite critical. No satisfactory separation can be obtained at lower or at higher concentrations.

II Procedure A) Determination of UBBC The filter discs were arranged in a stack with one cellulose-nitrate disc which was previously immersed in distilled water, on top of three DE-81 discs. The stack was placed in the "millipore" filter holder and washed with glass distilled water before use.

Duplicate samples of the serum (0.01 ml each) were incubated for 30 min at 37 (with excess of 57Co B-12 (100 pg/0.01 ml) and 0.2 ml 0.1 M Sodium Borate buffer (pH 8.5).

After incubation, the mixture was diluted to 10-12 ml with the borate buffer and passed by applying vacuum through the filter stack. The excess unbound 57Co B-12 was removed by washing the filter twice, with 10 ml of the same borate buffer. The unsaturated B-12 binding capacity (UBBC) 9 expressed in pg of 57Co B-12 bound per ml of serum, was calculated from the radioactivity retained by the stack.

B) Determination of TC-I, II and III binding capacity The duplicate samples of serum treated as described for the determination of UBBC were passed through the filter stack by applying vacuum. The excess unbound 57Co B-12 was removed as described above. Under these conditions TC-II is selectively and quantitatively adsorbed onto the cellulose-nitrate filter, while both TC-I and TC-III are adsorbed onto the DE-81 filters. After the filter stack was washed to remove the excess of 57Co B-12, the cellulose-nitrate filter was removed and counted (the first count). This count represents the unsaturated binding capacity of TC-II. The DE-81 filter stack was washed with 5 ml borate buffer and counted (the second count). This count represents the unsaturated binding capacity of TC-I and TC-III remaining on the DE-81 filter discs.

Transcobalamins I and III were separated by washing the DE-81 filter stack with 15 ml of 0.05 M monopotassium phosphate solution (pH 4.6). The stack was again counted (the third count). This count represents the unsaturated binding capacity of TC-I adsorbed on the stack after TC-III was removed by the monopotassium phosphate solution. The unsaturated binding capacity of TC-III is given by the difference between the second and third counts.

The results obtained by the above procedure were checked with a number of the established laboratory procedures known in the art and a good agreement was obtained. The entire procedure according to the present invention can be carried out in about one hour and many samples can be tested simultaneously. Thus this novel method provides an important novel clinical test which is of great diagnostic value and which permits one to obtain results in an easy, speedy and efficient manner.

It ought to be stressed that various attempts have been made to separate transcobalamins by DEAE cellulose-chromatography. Various authors have reported experiments at pH 5.8 with 0.1 M sodium phosphate; at pH 6.35 with 0.06 M phosphate buffer; at pH 6.2 with 0.075 M phosphate buffer; at pH 6.3 with gradient of phosphate buffer 0.06 M and 1M NaC1; a gradient of 0.01 M phosphate buffer (pH 8.0) and 0.3 M (pH 4.5). None of the above separation procedures was useful for an acceptable quantitative separation of the two transcobalamins I and III. The results obtained with sodium phosphate buffers, with monosodium phosphate and with potassium phosphate buffers were inconsistent and did not give the required separations. The concentration of 0.05 M monopotassium phosphate is quite critical.It may vary from about 0.045 to about 0.55, but at lower or higher concentrations inferior separations of TC-III from TC-I are obtained. The high pH of the borate buffer is a requisite for the selective adsorption of the TC-II on the cellulose nitrate filter.

Instead of the DEAE-cellulose filters there may be used DEAE-Sephadex mini-column.

The filter media used according to the above description can of course be used in column form.

The present invention also relates to test means in kit-form, comprising the necessary selective separation means, such as filter-column or stack, chemicals for the required solutions and 5 Co Vitamin B-12 solution.

Results obtained indicate that various pathological changes can be readily differentiated by means of the results obtained by the above method of determination of TC-I, TC-II, and TC-III.

Extensive experiments were carried out with patients having various types of disease. The procedure used was as set out above. The results of the determinations is given in the following. The following summary of the results is grouped as follows: Group 1: Deals with normals.

Group 2: Deals with chronic myeloid leukemia (CML) and promyelocytic leukemia (APL).

Group 3: Deals with Polycythemia vera (PV) and leukocytosis.

Group 4: Deals with acute leukemia, Hodgkins disease and lymphoma.

Group 5: Deals with hepatocellular damage.

a) Group 1: Normals Table - A No Patient B12 UBBC TCI TCII TCIII Identification pg/ml pg/ml pg/ml pg/ml pg/ml 1 E.G 700 1884 301 1260 283 2 Y. 570 1764 317 1112 335 3 Y.A 650 2230 356 1696 178 4 A.Z 870 1605 224 1012 369 5 R.M 950 2058 205 1462 391 6 R.Z 550 1925 212 1501 212 7 S.B 800 1720 190 1204 326 8 A.A 500 1360 136 984 240 9 Z.Y 900 1760 229 1355 176 10 O.Y 540 1560 203 843 514 11 H.D 700 1400 196 868 336 12 P.M 750 1500 120 1185 195 13 A.H 700 1484 268 905 311 14 S.A 660 1545 171 1019 355 15 B.A 700 1760 246 1144 370 16 R.A.H 700 1500 165 945 611 17 P.G 800 1588 159 1032 397 From Table A, one can define the ranges of Vitamin By 2, UBBC and transcobalamins in normal cases to be as follows: B12 500-950 pg/ml UBBC 1300-2250 pg/ml TCI 100-350 pg/ml TCII 800 1700 pg/ml TCIII 175 - 600 pg/ml b) Group 2: CML and APL Table - B No.Patient B12 UBBC TCI TCII TCIII Remarks Identification pg/ml pg/ml pg/ml pg/ml pg/ml 1 R.M 1500 6098 3780 1255 1063 2 A.R 3000 6823 4571 1500 752 3 S.A 2300 6352 3898 1674 780 4 c.P 4000 3623 2174 1196 253 5 Z.S 1300 3085 740 1666 679 in remission 6 A.Y 800 2235 290 1230 715 in remission 7 P.H 1000 2117 509 1025 583 in remission 8 A.l 1600 3970 1192 1627 1151 9 Y.M 1140 3394 1086 1459 849 10 C.Z 4000 2945 1537 1030 878 11 Z.B 1400 2747 1100 1330 317 12 B.A 2750 6461 3941 1163 1358 13 D.T 3000 6740 3628 1550 1562 14 R.A 3200 3660 1756 1574 330 In CML and APL cases there is elevation in UBBC, due to increase in TCI binding capacity, resulting in high serum B12 levels.

The increase in TCIII binding capacity is an expression of the chronicity of the disease, because of the more mature cells present in the population which produce mainly TCIII. The TCI binding capacity decreased during chemotherapy and this serves as a reliable criterion in the evaluation of the effect of the therapy. Patients in remission, show normal to slightly elevated ranges of TCI (patients Nos. 5-7). Thus, the test for TCI contributes to monitoring the course of chronic myeloid leukemia (remission, relapse and acute crisis) and the response to chemotherapy.

c) Group 3: PV and leukocytosis cases Table C Polycythemia vera (PV) and leukocytosis No Patient Remarks Identi- B12 UBBC TCI TCII TCIII fication pg/ml pg/ml pg/ml pg/ml pg/ml 1 M.P 400 1933 270 870 793 2 M.S 1250 3147 440 1320 1387 3 V.H 700 3352 370 969 2013 500 2941 299 964 1678 following chemotherapy 4 P.Y 900 3352 335 1173 1844 5 G.M 870 2529 227 1466 836 6 A.C 400 2076 228 1079 769 7 Y.Y 650 2176 148 961 997 8 S.M 550 3384 376 1522 1486 9 B.A 750 6461 356 1609 4496 10 M.P 900 2424 387 1284 753 11 B.A 750 2852 370 1369 1113 12 K.P 400 2360 295 979 1086 950 1529 229 902 339 following chemotherapy 13 A.F 700 2289 183 1533 572 14 CI 200 1970 177 1319 474 15 I.H 370 2294 137 1468 689 16 A.A 700 2117 296 1587 234 17 H.P 800 2000 280 1040 680 18 C.M 1000 2424 387 1405 632 19 C.Z 810 1888 170 1379 339 20 A.I 400 2613 236 1672 705 21 M.G 900 1558 202 898 460 In PV and leukocytosis there is elevation in UBBC due to increase in TCIII binding capacity.

No changes were noticed in B12, TCI or TCII.

In active PV (PV in relapse) associated with increased leukocyte concentration there is an increase in TCIII serum concentration (patients Nos 2,3,4,8,9,11 and 12). In the non-active PV state with normal leukocyte concentration, TCIII is normal to slightly elevated (patients Nos 1, 13-21). The TCIII binding capacity decreases during chemotherapy (patients Nos. 3 and 12). Thus, the test for TCIII contributes to monitoring the course of active (relapse) PV stages, the response to chemotherapy treatments, and monitoring the non-active PV stages as well. More important, serum TCIII binding capacity determination helps in differentiation of leukemoid reactions and conditions manifested by non-leukemic leukocytosis.

d) Group 4: Acute leukemia, Hodgkins disease and lymphoma cases Table-D Acute leukemia cases No Patient B12 UBBC TCI TCII TCIII Remarks Identi fication pg/ml pg/ml pg/ml pg/ml pg/ml 1 lA 1000 3647 291 2918 438 2 P.M 730 3763 452 2747 564 3 P.N 900 7568 203 6760 605 900 4018 201 3335 482 Following chemotherapy 4 K.H 750 6000 400 5180 420 750 3037 273 3581 183 Following chemotherapy 450 2545 127 2188 230 Following chemotherapy 5 M.S 270 2935 376 2431 410 370 1900 171 1349 380 Following chemotherapy 6 Z.H 850 3364 471 2422 471 700 2360 306 1652 402 Following chemotherapy 7 M.B 900 3030 121 2545 364 300 2000 140 1540 320 Following chemotherapy 450 1900 285 1240 375 Following chemotherapy 500 1360 136 984 240 Following chemotherapy 8 B.A 475 2650 291 1829 530 600 2063 228 1583 247 Following chemotherapy 9 H.M 1000 2300 254 1771 276 500 1700 173 986 571 Following chemotherapy 10 Z.I 580 2739 109 2492 137 670 1834 129 1467 238 Following chemotherapy 700 2000= 258 1442 300 Following chemotherapy 900 1760 229 1355 176 Following chemotherapy 11 H.H 200 2360 277 1959 123 870 1930 368 1258 674 Following chemotherapy 12 N.A.A 1200 2000 180 1460 360 Protracted course 13 A.H.N 650 2100 280 1400 420 Protracted course 14 ZI 600 1760 119 1330 311 Protracted course 15 G.M 1070 1868 280 1309 280 Protracted course e) Group 5:Hodgkins disease and lymphoma cases Table-E No Patient B12 UBBC TCI TCII TCIII Remarks Identi fication pglml pg/ml pg/ml pg/ml pg/ml 1 B.S 950 5300 380 4500 420 500 1475 163 1012 300 Following chemotherapy 2 Z.A 720 4411 486 3514 411 3 I.P 700 2615 235 2119 261 4 A.A 900 3600 180 3096 324 5 V.V 500 4176 126 3499 551 6 V.A 1000 5100 204 4384 512 7 L.H 850 4650 372 3787 491 8 A.A 450 3500 175 2905 420 9 K.I 700 4900 434 3800 666 10 S.V - 4500 180 4005 315 11 I.S - 2910 175 2270 465 12 S.B - 1500 150 1020 330 Protracted course 13 S.Z - 2100 147 1680 273 Protracted course Tables D and E relating to acute leukemias, Hodgkins disease and lymphomas in which there is increase in UBBC due to elevation in TCII binding capacity. No changes were noticed in B12, TCI or TCIII.The increase in TCII is in direct proportion to the acuteness of the disease.

"Increase in serum TCII binding capacity without a change in Vitamin B12 level may indicate an acute proliferation of malignant cells of any kind (such as acute leukemia, Hodgkins disease, lymphomas, etc). This finding may be useful in the recognition of rapid cell prolifera tion in malignant lymphoma and acute nondifferentiated leukemias. The TCII binding capacity decreases during chemotherapy and thus serves as a reliable criterion in the evalua tion of the effect of the therapy. Patients during the protracted or remission course show normal ranges of TCII. However, during the proliferation of the malignant cells (the relapse stage) increase in TCII binding capacity is noticed.Thus, the test for TCII contributes to the monitoring of the relapse course of acute leukemias, Hodgkins disease, lymphomas, etc., the response to chemotherapy treatments and monitoring the protracted course or remission as well.

f) Group 5: Hepatocellular damage It is well established that increase in serum Vitamin B12 bound mainly to TCII is characteristic to hepatocellular damage. The B 12 released from the damaged liver cells saturates TCII and part of the TCI. As a result, serum binding capacity (UBBC) is very low while endogenous B12 bound to TCII is increased. Since the filter-stack technique determines the UBBC of the binders, in hepatic diseases the TCII will be very low. This phenomena is already well recognized and accepted as a valuable diagnostic aid.

Summary Determination of serum transcobalamins binding capacity is useful in diagnosis of the following diseases: Disease Vitamin UBBC Binding Capacity B12 of whole serum TCI TCII TCIII (1) CML and APL elevation elevation elevation normal elevation PV and leukocytosis normal elevation normal normal elevation AML, Hodgkins normal elevation normal elevation normal disease lymphoma Hepatocellular elevation decrease normal decrease normal damage (1) in chronic cases Serum transcobalamins binding capacity determination is also useful in monitoring the relapse course of these diseases, the response to chemotherapy treatments and monitoring the protracted or remission courses as well.

In summary, the three transcobalamins undergo specific quantitative changes during certain clinical pathological conditions. The research done on this subject during the last few years has proved beyond any doubt the clinical significance of the changes in the transcobalamins binding capacity. The determination of the various serum transcobalamins binding capacity is today an important tool in diagnosis as well as in evaluation of the effects of treatment.

WHAT WE CLAIM IS: 1. A process for the quantitative determination of each of the three transcobalamins TC-I, TC-II, and TC-III in serum, which comprises incubating a predetermined quantity of serum with a solution of 57Co Vitamin B-12, passing the resulting solution at a pH of about 8.5 through adsorption means adapted to selectively adsorb TC-II in the form of a filter of cellulose carrying highly polar substituents or of a small adsorption column; adsorbing the TC-I and TC-III constituents of the resulting solution on a filter or small column of DEAEcellulose; selectively desorbing the TC-III using a monopotassium phosphate solution of about 0.05 M and a pH of about 4.6, and determining the radioactivity of each of the three transcobalamin fractions thus obtained, indicating the individual and total unsaturated B-12 binding capacity (UBBC) of the three transcobalamins.

2. A process according to claim 1, wherein the incubation is effected with 0.1 M sodium borate buffer of pH about 8.5.

3. A process according to claim 1 or 2, wherein the mixture is applied to a filter stack or small column by application of reduced pressure.

4. A process according to any of claims 1 to 3, wherein the unbound 57Co B-12 is removed from the stack by means of borate buffer.

5. A process according to any of claims 1 to 4, wherein the TC-II is adsorbed on a cellulose nitrate filter or column.

6. A process according to any of claims 1 to 5, wherein the TC-I and TC-III are adsorbed on DEAE-cellulose filter discs.

7. A process for the quantitative determination of TC-I, TC-II, and TC-III, substantially as hereinbefore described in the Example.

8. A kit for the quantitative determination of TC-I, TC-II, and TC-III, comprising in combination 57Co B-12 solution, adsorption means for the separation of TC-II from combined TC-I and TC-III in the form of a filter of cellulose carrying highly polar substituents or of a small adsorption column; a filter or small column of DEAE-cellulose; monopotassium phosphate solution of about 0.05 M and a pH of about 4.6, and a borate buffer of pH about 8.5.

9. A kit according to claim 8, wherein the adsorption means of the separation of TC-II from combined TC-I and TC-III is a cellulose nitrate filter placed on top of a stack of DEAE-cellulose filters of adequate thickness to quantitatively adsorb both TC-I and TC-III.

10. A kit according to claim 8 or 9, wherein the borate buffer is 0.1 M.

11. A kit according to any of Claims 8 to 10, wherein the 57Co B-12 is of an activity of from 135-200 uCi/ug.

12. A kit for the individual determination of TC-I, TC-II, and TC-III, substantially as hereinbefore described in the Example.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. (1) in chronic cases Serum transcobalamins binding capacity determination is also useful in monitoring the relapse course of these diseases, the response to chemotherapy treatments and monitoring the protracted or remission courses as well. In summary, the three transcobalamins undergo specific quantitative changes during certain clinical pathological conditions. The research done on this subject during the last few years has proved beyond any doubt the clinical significance of the changes in the transcobalamins binding capacity. The determination of the various serum transcobalamins binding capacity is today an important tool in diagnosis as well as in evaluation of the effects of treatment. WHAT WE CLAIM IS:

1. A process for the quantitative determination of each of the three transcobalamins TC-I, TC-II, and TC-III in serum, which comprises incubating a predetermined quantity of serum with a solution of 57Co Vitamin B-12, passing the resulting solution at a pH of about 8.5 through adsorption means adapted to selectively adsorb TC-II in the form of a filter of cellulose carrying highly polar substituents or of a small adsorption column; adsorbing the TC-I and TC-III constituents of the resulting solution on a filter or small column of DEAEcellulose; selectively desorbing the TC-III using a monopotassium phosphate solution of about 0.05 M and a pH of about 4.6, and determining the radioactivity of each of the three transcobalamin fractions thus obtained, indicating the individual and total unsaturated B-12 binding capacity (UBBC) of the three transcobalamins.

10. A kit according to claim 8 or 9, wherein the borate buffer is 0.1 M.